What does a Ford diagnostic test. Test for on a car?

I've recently took my car in for some warranty work to be done.( For free, well I thought).
But the guy at ford has rang me up saying I owe them £100 for the diagnostic test which has told him its the washer pump thats gone.
Can the test show its the washer pump thats gone. Or has he looked under bonnet and tryed to scam me out of 100 pound?

Read the warranty clause on your car. Some warranties do not include labor charges, only parts.

Why did you take the vehicle in? If it was to have the washers repaired they can charge you time to determine what was wrong. It could have been the pump was bad or that the wiring or washer switch was bad. They would have needed to remove the tire well splash shield on most vehicles to get to the pump and wiring so a labor charge should be expected.
If you didn't tell them to do anything concerning the washers not working they should have called you for permission to do so.
The question is why you thought you needed a diagnostic test and for what reason.

I own a garage.uk £100 is a lot of money when it should be free… Never seen any type of diagnosis for a washer pump!

You should not be paying for them to diagnose a fault that is covered under the warranty

If the car is not under warranty, then it's reasonable to expect a diagnostic charge for any repair. With that said £100 is pretty steep to just tell that the windshield washer pump is out.

Be very very surprised if diagnostic check would include a washer pump! Yes ford main dealers DO charge £100 to run a diagnostic check ( I asked and declined having it carried out for free somewhere else) if we have an issue with car and its being looked at under warranty? Then any checks they carry out will be at their cost.Subject to small print other items can be covered too e.g.Labor.parts.
do check with Ford motor co about diagnostic check for locating washer pump fault! Would have thought an average intelligence mechanic can check that if not working without needed an expensive computer check.
if we agreed to extra costs before starting work? Then sadly the high Ford ( rip off fee) charge will be mandatory. I nearly got caught for asking for this test but luckily asked price.( thought it was free) so cancelled. Dealer asked who I was going to get fault located with running a test.Again luckily I knew a man whom can and did check for me for free.

No a diagnostic test will not tell you the washer pump has failed. Using it will.
I hate this charge for a diagnostic check thing.
You do not expect to pay extra for the use of a spanner or a ramp at a garage.
A diagnostic system is just a workshop tool.
With modern cars one that is required.
Use of metric spanners was never a extra charge when cars went metric.
I use a small guy who just plugs in as part of his service
I would expect a check under waranty to be free but dealers vary in what they charge for.

If the automobile isn't underneath guarantee, then it's cheap to expect a diagnostic charge for any repair.Therewith aforesaid £100 is pretty steep to simply tell that the screen washer pump is out.

Nope. Not all is computer diagnosed and took a mechanic to tear your car apart and to do oldschool checking with a volt meter hince the 100 quid

Contact the ford corperate offices in your area if it was under warrenty it should be covered